1. Field of the Invention
This invention relates to interconnect systems and more particularly to interconnect systems for multiple inkjet pens in an inkjet printer.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Inkjet printer/plotters and desktop printers, such as those sold by Hewlett Packard Company, offer substantial improvements in speed over the conventional X-Y plotter. Inkjet printer/plotters typically include a pen having an array of nozzles. The pens are mounted on a carriage which is moved across the page in successive swaths. Each inkjet pen has heater circuits which, when activated, cause ink to be ejected from associated nozzles. As the pen is positioned over a given location, a jet of ink is ejected from the nozzle to provide a pixel of ink at a desired location. The mosaic of pixels thus created provides a desired composite image.
Inkjet technology is now well known in the art. See, for example, U.S. Pat. Nos. 4,872,027, entitled PRINTER HAVING IDENTIFIABLE INTERCHANGEABLE HEADS, issued Oct. 3, 1989, to W. A. Buskirk et al. and U.S. Pat. No. 4,965,593, entitled PRINT QUALITY OF DOT PRINTERS, issued Oct. 23, 1990, to M. S. Hickman, the teachings of which are incorporated herein by reference.
Recently, full color inkjet printer/plotters and desktop printers have been developed which comprise a plurality of inkjet pens of diverse colors. A typical color inkjet printer/plotter has four inkjet pens, one that stores black ink, and three that store colored inks, e.g., magenta, cyan and yellow. The colors from the three color pens are mixed to obtain any particular color.
The pens are typically mounted in stalls within an assembly which is mounted on the carriage of the printer/plotter. The carriage assembly positions the inkjet pens and typically holds the circuitry required for interfacing to the heater circuits in the inkjet pens.
Conventionally, a carriage assembly consists of four pen stalls to align the inkjet pens, four pen clamps to hold the inkjet pens in the pen stalls, a printed circuit board having the circuitry for interfacing to the heater circuits in the inkjet pens, and four separate flexible circuits interconnected between the printed circuit board and electrical contacts on the inkjet pens. Each of these separate parts are conventionally assembled piece by piece with screws fastening the parts individually to a housing to form a carriage assembly. Assembly of these individual parts is a difficult and expensive process and special tools are required to properly align the parts.
The carriage assembly moves during printing and for quick responsiveness, it is required that the overall carriage assembly be lightweight, which results in a relatively fragile carriage assembly. If a conventional carriage assembly is accidentally bumped or one of its components fails, then repair for a conventional carriage assembly is costly, because of the multitude of individual parts and the difficult alignment process.
Conventionally, in a carriage assembly, a separate flexible circuit is used to interconnect each inkjet pen to the associated printed circuit board. The flexible circuit is made with a polyester or polyimid material such as a Mylar or Kapton substrate onto which multiple conductors are deposited. A color inkjet printer with four inkjet pens requires four separate flexible circuits.
The use of four separate flexible circuits has the disadvantages of: 1) high cost, due to the need to manufacture and stock the multiple separate flexible circuits; 2) difficulty of assembly, because of the need to route in the carriage assembly and precisely align each of the separate flexible circuits to each of the pen housings; 3) cost of assembly because the separate flexible circuits need to be separately interconnected with the printed circuit board; and 4) the need to provide separate grounds for each separate flexible circuit.
As there is typically limited interconnect area for grounds, having separate grounds for each flexible circuit limits the number of ground interconnects available for an inkjet pen. Separate grounds for each flexible circuit prevents sharing of a common ground plane for all the inkjet pens, which would be advantageous, because ground plane sharing assists in maintaining all the heater circuits in the inkjet pens at the proper ground potential regardless of which heater circuits are activated. In a conventional device, separate ground are provided for each inkjet pen, which can cause ground fluctuations and inkjet pen performance degradation, if a large number of heater circuits in one inkjet pen are activated.
Other conventional approaches to inkjet electrical interconnect include the use of edge connectors that have the disadvantages of high cost and low interconnect density.
Accordingly, there is a need in the art for an improved interconnect system that reduces cost, is easier to assemble and align, and provides ground plane sharing for all of the inkjet pens.